From mboxrd@z Thu Jan 1 00:00:00 1970 From: Brad Campbell Subject: Re: Raid5 to raid6 reshape or recreate? Date: Thu, 14 Aug 2014 14:06:11 +0800 Message-ID: <53EC51D3.9020204@fnarfbargle.com> References: <53EAB9F1.5030905@gmail.com> <53EC2D0E.2070402@fnarfbargle.com> <53EC36A8.7090308@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <53EC36A8.7090308@gmail.com> Sender: linux-raid-owner@vger.kernel.org To: Ram Ramesh Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 14/08/14 12:10, Ram Ramesh wrote: > On 08/13/2014 10:29 PM, Brad Campbell wrote: >> On 14/08/14 01:25, Ram Ramesh wrote: >> >>> On a slightly different topic, will it be faster after a disk >>> fail/replacement as opposed to raid reshaping? >> >> Much. >> I just re-striped a RAID6 changing the chunk size from 128k to 64k. >> This took 12 days all up. It's the seeking that kills it. To replace a >> disk or do a resync on the same array takes less than 10 hours. >> >> >> > I am curious. Why do you have to change chunk size? What is the > benefit/advantage? When I initially selected 128k it was for a stripe of 8 chunks (10 disks) and for a workload that contained lots of fairly big streaming writes and reads. The array has since grown to 12 chunks (14 disks) and the workload turned out to be a lot more random than I initially had profiled, so I re-striped to attempt to reduce the amount of RMW happening on the disks. It may well be academic, but it's a lot easier to find 768k to write in one action than 1.5M. ... and probably because I could.